linux-kernel - Re: [PATCH 0/4] mm,memory_hotplug: allocate memmap from hotadded memory

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Message-ID: <20190403083359.vqbzy5krjfzfjedx@d104.suse.de>
Date:   Wed, 3 Apr 2019 10:34:00 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
        dan.j.williams@...el.com, Jonathan.Cameron@...wei.com,
        anshuman.khandual@....com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 0/4] mm,memory_hotplug: allocate memmap from hotadded
 memory

On Wed, Apr 03, 2019 at 10:12:32AM +0200, Michal Hocko wrote:
> What does prevent calling somebody arch_add_memory for a range spanning
> multiple memblocks from a driver directly. In other words aren't you
> making  assumptions about a future usage based on the qemu usecase?

Well, right now they cannot as it is not exported.
But if we want to do it in the future, then yes, I would have to
be more careful because I made the assumption that hot-add/hot-remove
are working with the same granularity, which is the case right now.

Given said this, I think that something like you said before, giving
the option to the caller to specify whether it wants vmemmaps per the
whole hot-added range or per memblock is a reasonable thing to do.
That way, there will not be a problem working with different granularities
in hot-add/hot-remove operations and we would be on safe side.

-- 
Oscar Salvador
SUSE L3